Filament structure



Nov. 10, 1953 G. J. AGULE FILAMENT STRUCTURE 2 Sheets-Sheet 1 Filed June 21, 1951 FIG. 6

INVENTOR GEORGE J.

@JLE a m ATTORNEY FIG. 5

NOV. 10, 1953 J, AGULE 2,659,023

FILAMENT STRUCTURE Filed June 21, 1951 2 Sheets-Sheet 2 INVENTOR ciEoRGEJ. A LE BY ,.4,/ ATToRriEY Patented Nov. 10, 1953 2,659,023 FI-LAMENT STRUCTURE George J. Agule, Stamford, (301111., assignor to Machlctt Laboratories, Incorporated, Springdale, Conn., a corporation of Connecticut Application June 21, 1951, Serial No. 232,810

9 Claims.

This invention relates to a novel filament structure for use in high power vacuum tubes. In particular this invention concerns a filament which will withstand severe heating, electromagnetic forces and mechanical vibration effects without materially changing tube characteristics.

It is a primary object of this invention to combine the good features of the free hung squirrelcage filament and the spring tensioned, center mast type filament in a construction superior to both of these structures. The free hung filament is desirable because of its light weight and its efiicient electron emission qualities. The center mast construction has desirable features because the tension supplied to the filament strands prevents their sagging and bowing and because of the overall strength of the structure. My novel filament construction consists of a stranded filament and a center mast structure coaxially located within the filament circle but preferably not extending the full length of the filament. At least one pair of close spaced, radially extending annuli is affixed to the center mast. From these annuli ties of fine wire extend to the filament strands. Each fine wire tie is preferably looped around an individual strand and returned to the same annulus. In a filament structure in which adjacent strands carry current in opposite directions, the fine tie wires from one annulus extend to alternate filament strands and the tie wires from the other annulus extend to the other filament strands. Connecting tie wires from strands carrying current in opposite directions to different annuli avoids connecting points at different potentials to the same member. The radial annuli are insulated from the center mast and from one another so that there can be no shorting from one strand to another through the ties.

It is an object of my invention to prevent bow ing of the filament due to electric forces. In the most common type of filament structure the electromagnetic forces produced in adjacent strands by current which flows through these strands in opposite directions tends to drive these strands apart. Each strand tends to be repelled by its adjacent strands. The circular arrangement of filament strands places any given strand outside of a chord drawn between its adjacent strands. Thus the electromagnetic forces tend to cause a bowing out of the filament strands so that the filament as a whole tends to assume a barrel shape. Such change in shape obviously alters the tube characteristics and possibly may result in shorting to the grid. The old center mast type structure exerts a pull along the length of each filament strand which tends to oppose the bowing forces, but the free hung type filament has no such means of opposition. By my invention, however, the fine wire ties act to hold the filament strands against bowing outward so that, by proper axial location of the ties, mechanical opposition to the bowing may be supplied in that region where the electromagnetic forces normally have their greatest effect.

It is another object of my invention to prevent sagging or warping of the filament due to heat efiects. Free hung filaments have been particularly subject to sagging when used in a horizontal position. The heating effects cause sufficient softening of the filament to allow gravity to bend it out of its axial alignment. Thus shorting may eventually result. The old spring loaded center mast prevented such a result by supplying rigidity to the filament structure as a whole through the center mast structure. My invention accomplishes the same result in a similar manner but without such a bulky and complicated structure. My center mast, which extends axially within the filament strands is sufliciently sturdy to resist all forces tending to cause its misalignment, and the tie wires aflixed thereto prevent the filament from moving away from the center mast.

It is another object of my invention to permit the use of what amounts to long free hung filaments. Prior art structures for filaments have been limited in their length whether they have a free hung or a center mast type construction. In the free hung type structure the length has been limited by the strength of the filament strands relative to the weight of the filament in that the filament strands themselves have to oppose the gravitational forces tending to pull the filament out of alignment. In the center mast construction the difficulty lies in the bearing which is necessary to permit the axial movement of the center mast required for maintaining tension on the strands. This bearing like all bearings has to be made with clearances and tolerances. Thus the center mast has some play and is able to rotate a small amount around the bearing as a pivot point. In a short structure this small amount of rotation is not important. but the longer the filament, the more important its efiiect, i. e. the further the end of the filament from the bearing, the more it may deviate from the tubes axis. My center mast structure is not movable: hence it may be permanently and acfired on. the tubes axis. Thus, assumg ccurate alignment of the center mast, my slam ht may be much longer than any filalcnown to the prior art due to support from the center mast by means of the fine wire ties. The longer the filament the greater the number of levels at which support must be supplied.

It is another object of my invention. to prevent breakage of the filament due to mechanical vibration. Filament breakage may occur due to err.- cessive bumping or other rough mechanical handling of the tube. Most of this breakage may be traced to the filament momentarily striking the grid. Of course, this could be the result of too much play in the hearings in center mast structur It is often due to the relative flexbility of the free hung type structure. This lat-- ter type structure usually has a large amplitude of vibration which may be sufficiently large to permit the filament to momentarily sharply strike the grid structure. My invention prevents such an occurrence by the use of fine wire ties which restrict the radial movement of the filament strands.

It is another object of my invention to permit unrestricted axial expansion of the filament similar to that allowed a free hung filament. The spring tensioning of the strands in prior art center mast type structures take up any slack occurring in the filament due to expansion of the strands, but this effect depends upon the use of a spring. The use of a spring within vacuum tubes is subject to a great many difficulties, primarily because of the high temperatures en countered therein. The high temperatures within the tubes tend to cause relaxation. of the springs so that they no longer perform their tensioning function. Attempts to locate the springs in cool parts of the tube have minimized this effect somewhat, but they have necessitated enlargement of the tube and have led to other complications which may cause misalignment, such as the necessity of a long lever arm between the spring connection and hearing. The bearings involved in a spring tensioned, center mast type structure have also led to difficulties such as sticking of the center mast in the bearing. My structure avoids all uses of springs and bearings and is essentially a conventional free hung filament with extra support given by the center mast. The tie wires joining the strands to the center mast are suificiently flexible to permit the necessary differential expansion between center mast and filament without imposing strain upon the filament strands. Since non-moving parts are employed in my structure and since the annuli are securely mounted in a fixed position on the center mast, preferably by means hereinafter descibed, only the flexibility of the tie Wires per mite unrestricted axial expansion of the filament strands.

Another object of my invention is to obtain eficient electron emission from the filament. An advantage of the free hung filament over the old center mast filament is its ability to be sufficiently heated to emit electrons throughout its length, except immediately adjacent its support. In the old center mast type structure the relatively massive supports at either end of the filament structure tend to conduct heat away from both ends of the filament strands. Thus the filament is cooled below the emission temperature at both ends. My filament has a massive support at only one end as does the free hung filament and is tied to the center mast by means of ties of such cui'ate inc. i1

fine wire that they oifer an extremely high heat flow impedance path. Thus even at the tie connection points the filament strands will not be cooled sufficiently to prevent emission.

For a better understanding of this invention. reference is made to the following drawings:

Fig. 1 illustrates an electron tube in which my novel filament structure is employed shown in partial cross section.

Fig. 2 is an exploded cross-sectional view of one possible assembly for affixing the radially extending annuli to the center mast.

Fig. 3 illustrates a perspective view showing a portion of the filament a portion of the cen-- ter mast with tie connections therebetween.

Fig. i is an elevational view from. below of the filament structure such as illustrated in 3..

Fig. 5 shows an elevational view of an alter native type annulus to be employed at the center mast to which filament strands may be tied.

Fig. 6 is a side elevational view of the annulus shown in Fig. 5.

Fig. shows one means of afiixing multiple pairs of annuli to a center mast.

Fig. 8 shows another way to employ multiple pairs of annuli.

Referring to the drawings, Fig. 1 illustrates a large triode in which my invention is advantageously employed. The tube has an external anode IQ of cup shape whose lip is joined to a tu bular member H forming an extension of the anode folded back over the cup Ill. It is often convenient to extend this tubular member H by tubular member is which also surrounds anode cup 3 and extends below the bottom thereof. Between the cup it and the tubular members H and i2 lies another tubular member :3 which extends to the region of the junction of members it and Ii but does not touch these members. the ends of tubular members l2 and 93 adjacent the bottom of anode cup it, annular members 2 and Ill are aiiixed. ihese annular members may be of such shapes as may be sealed together conveniently to form a cavity at the base of members 12 and [3. In operation of the tube, cooling water may be forced through the hole in annular men.- ber I i, up between anode cup It and tubular member it, down between tubular members it and ii and tubular member 13, and out through holes through annular member i It is also often convenient to bring an exhaust tubulation lilo from the anode cup out through hole in annular member Hi. The tube itself has a radially extending anode terminal I"? which is advan tagcously joined to tubular member i H.

An annular grid terminal H parallels anode terminal 16 and is separated therefrom by a column composed of Kovar collars IB and i9 and glass ill The grid is afiixed to the grid ter-- urinal l'i by means of screws M or similar means which hold the grid support collar 22 against the grid terminal ill. The grid may advantageously be of the spiral type having its active portion 23 wound spirally around grid support rods 25 which are parallel to the tube axis and affixed to the grid support collar 22. The opposite end of the grid may be aifixed to a metallic plate 25.

Filament terminals 25 and 21 are located at difierent axial levels parallel to the anode terminal iii and the grid terminal ll. Filament terminal 25 is an annular member and is separated from the grid terminal ll by a column composed of Kovar collars 28 and 29 separated by glass 38 and terminals 26 and 2! are separated by a column composed of Kovar collars 3i and 32 separated by glass ring 33. Aflixed to: terminal which extends towards the. anode cup. l0. Afiixed to filament terminal 21 is tubular support which also extends toward the anode cup and lies within and coaxial with support 34. Both support 34 and support 35 may have inward extending radial flanges 34a and 35a respectively. Filament support rods 36 are affixed to. their re.- spective supports in a circle and their filament support members extend toward the anode cup Hi. It is necessary for the support rods which extend from support 35 to pass through flange 34a without contacting said flange so that holes are made therein large enough for the insulated passage of rods 36. The support rods 36 have radially extending clips 37 which connect the filament strands 38 and 39 to support rods 36. The tube as thus far described is similar to the tube described in my patent application Serial Number 185,645, with the possible difference that the filament herein may be longer.

The novel portion of my tube is built around an axial center mast 4! which is advantageously supported at only one end. This end of this novel center mast may be ailixed to any sturdy portion of the tube envelope or support structure. It may be conveniently afiixed to a cross member 42 which in turn may be mounted against a planar surface, such as is afforded by the lower end of filament support member 35, and held in place by screws 43 or other means. Accurate alignment of the center mast permits the use of equal length tie wires 44 and 45 all the way around the center mast which provides a good balance of forces acting upon the various filament strands. These tie wires are advantageously affixed to parallel annuli 46 and 41 mounted on the center mast M with both ends of each tie affixed to the same annulus. The tie wires are looped around the filament strands 38 and 39 in which may be formed small bends 36a or 39a. If they are thus tied to the center mast with little slack or play left in the wire loop, the filament strands will be constrained against distorting electrical, mechanical and gravitational forces. The fineness of the tie wires makes them have high heat fiow impedance so that the filament strands will not be cooled while held in place.

Referring to Fig. 2. an exploded view of a typical assembly for holding the radial annuli in place on the center mast is shown in cross section. The diameter of the end 48 oi. the center mast is materially decreased forming shoulder 49. Tubular insulator 5t fits over this portion of reduced diameter 58 end has a radial flange 51 at one end which rest against shoulder 49. Annulus as over tubular insulator 58 and rests against radial fiange 5i. Insulator ring 52 fits over tubular insulator and rests against annulus it. Planar annulus 4'! fits over tubular insulator it and rests against insulator 52. Ring insulator 53 fits over tubular insulator 50 and rests against annular member 4'1. Threaded nut 54 engages threaded portion 48a of the center mast and may be tightened against insulator 53, thereby holding the assembly in place; Thus, the assembled annuli 46 and 4'! are mutually insuated from one another and each of them is insulated from the center mast.

Although the construction as specifically described and pictured in Fig. 2 provides one convenient assembly for accomplishing my invention, there are many others which may be employed. For instance, the flange ii insulator 50 migh be at. the location of eit in in u tor 5.2.: 1 rin insulator 5,3, in which case flange 5| weuld be a, rin Other means of accomplishing the same end will be obvious to any one skilled in the art. Likewise means engaging the center mast, other than the nut 54 may be used to hold the insulated assembly in place.

Figs. 3 and 4 show in greater detail the parallel annuli, ararngement, and the ties to the various filament strands. It may be noted that annuli of non-conducting material might be substituted for the metallic annuli thus simplfying the insulation problem. However, metallic annuli are preferred because of their relative ease of fabrication and th ir greater flexibility in use.

Figs. 5, and 6 illustrate a modified annulus which might be used instead of the simple circular annuli shown elsewhere. This spider-like member 46 has radial legs 55 at the outer edge of the annulus. The sides of these legs may be folded back to form tabs 5511 which may be advantageously crimped over tie wires in order to hold them in place. In practice the spider type of structure might be preferable to the simple circular annulus such as 45 or 41 shown in Figs. 2, 3 and 4 because the simple annulus makes it necessary to lace a continuous piece of fine wire through holes in the annulus, to weld or solder the ends of the wire to the annulus or to employ some other equally inconvenient means of affixing the tie wire. It is to be understood, however, that the use of tie wires is not restricted to loops around the filament strands tied at both ends to an annulus, although such an arrangement is advantageous in that it makes it easier to make each loop taut. Any means of affixing fine tie wire to the filament strand and to the annuli at the center mast is within the scope and spirit of this invention.

Sometimes for the purpose of added support in the case of extra long filaments, it may be necessary to employ fine wire ties at several axial levels so that more than a single pair of annuli is needed. Pairs of annuli may be introduced at various axial levels along the center mast by various means.

Fig. '7 shows one possible means of using multiple pairs of annuli. Here the center mast 4! has its diameter reduced at one end 56 forming shoulder 51. Over the reduced diameter portion fits an insulated assembly consisting of a tubular insulator 58 having a radial flange 58a which rests against shoulder 51 and against which radially extending annulus 55 is placed. Annulus 60, identical in shape to annulus 59, is separated therefrom by annular insulator 5! which fits over insulator 58. Insulator 62 is placed over tubular insulator 58 on the side of annulus Fill remote from annulus 59. An extension 63 of center mast 4| which may be of the same general diameter is tapped 64a at end 84 along its axis and engages threaded portion 56a of the reduced diameter portion of shaft 4|. The end 54 extension member 63 presses against insulator $52, which is made to extend below insulator 5d, and holds the assembly of flanges and insulators in place.

Extension 63 also has a reduced diameter portion 55 at its opposite end thereby forming shoulder 66. Over portion 65 is placed tubular insulator 61 having a radial flange 61a which bears against shoulder 55. Annuli 68 and 69 are separated by annular insulator If! and bear against flange 67a on the opposite side of annulus 6.8. Insulator H is placed on the opposite side of annulus 69 so that it extends below tubular insulator GT. Nut 12 engages threaded por tion 65a of the reduced diameter section 65 and supplies the necessary pressure to hold the complete assembly in place.

Opposing shoulders similar to shoulders 51 and 64 in Fig. 7 are necessary at the joints in a sectional type of center mast in order to hold the insulat-ed annuli assemblies in place. These shoulders need not be formed by reduction of mast diameter as is done in the Fig. '7 construction, however, although this is probably the most convenient manner of producing shoulders. For instance, separate members forming radially extending shoulders might be affixed to the center mast sections by welding or brazing them in place. Further variations from the Fig. '7 construction may be achieved by attaching center mast sections together by means other than the engagement of threaded portions e. g., by soldering.

Fig. 8 illustrates another multiple insulated annuli arrangement. In this instance, the center mast M" is reduced in diameter, producing shoulder It at such. a point as to leave a long extension of reduced diameter T l. An insulated assembly similar to those previously described is employed. A tubular insulator 2'5 which has a radial flange a at one end is used and over it is fitted a pair of radially extending annuli I6 and H separated by an annular dielectric member. lhe annuli lie between dielectric ring it and flange 75a. Tubular separator 89 fits over center mast extension l4 and lies between adja cent pairs of insulated annuii. Tubular separator B5 is reamed a: at one end so that edge 82 is left to make contact only with insulator ii and not with insulator l5. Insulated assemblies generally designated. 33 and 54 are similar to those already described. They lie below separator 8i! and are separated atubular separator 85 similar to separator 8t. A nut 86 engages the thr aded portion l lo oi the reduced diameter oi the center mast and pressure is exerted against assembly 53:3, thence separator 85, thence assembly 35, thence separator 5d and finally to the assembly adjacent shoulder 13 against which the whole assembly is firmly held.

When separators are used between assemblies as in Fig. 8 the diameter or the shaft need not be reduced as long as the shaft furnishes a shoulder or stop means against which the successive assemblies and separators may be firmly held.

The term fine wire is used herein as a term of broad coverage with respect to the cross-secticnal shape of the wire. The wire may be a ribbon wire well as a more conventional round wire, and, in fact, a wire of any cross-sectional shape may be employed.

I claim:

1. In an electron tube having an anode and a filament within a vacuum envelope, a filament structure comprising a plurality of parallel filament strands circularly arranged and so connected that they permit a flow of current therethrough, a center mast supported at one end and located on the tubes axis, a close spaced pair of annuli extending radially from the center mast on which said annuli are mounted in a fixed pcsition, fine wire ties connecting filament strands to the annuli, ties of the same potential being afiixed to the same annulus, and means insulating the tie wires of one potential from the other tie wires.

2. In an electron tube having an anode and a filament within a vacuum envelope, a filament structure comprising a plurality of parallel filament strands circularly arranged and so connected that they permit a flow of current therethrough, a center mast supported at one end and located on the tubes axis, a close spaced pair of metallic annuli extending radially from the center mast on which said annuli are mounted in a fixed position, annular insulators insulating theannuli from the center mast and from one another, and fine wire ties connecting filament strands to the annuli, ties of the same potential being aifixed to the same annulus.

3. In an electron tube having an anode and a filament within a vacuum envelope a filament structure comprising a plurality of parallel filament strands circularly arranged and so con nected that they permit a flow of current therethrough, a center mast supported at one end and located on the tubes axis, a close spaced pair of metallic annuli extending radially from the center mast on which said annuli are mounted in a fixed position, annular insulators insulating the annuli from the center mast and from one another, and fine wire ties looped around the filament strands and ailixed on both sides thereof to the same annulus, ties of the potential being affixed to the same annulus.

4. In an electron tube having an anode and a filament within a vacuum envelope, a filament structure comprising a plurality of parallel filament strands circularly arranged and so con nected that they permit a fiow of current therethrough, a center mast supported at one end and located on the tubes axis, close spaced pairs of metallic annuli extending radially from the center mast at various axial levels on which center mast said annuli are mounted in a fixed position, annular insulators insulating the annuli from the center mast and from one another, and fine wire ties looped around the filament strands and afhxed on both sides thereof to the same annulus, ties of the same potential being affixed to the same annulus.

5. In an electron tube having an anode and a filament within a vacuum envelope, a filament structure comprising a plurality of parallel filament strands circularly arranged and afiixed to support and terminal means at one end, the other ends converging and terminating in parallel portions which are fixed together, a center mast of refractory metal supported at one end, located on the tubes axis and extending toward the converging portion of the filament strands, a close spaced pair of metallic annuli extending radially from the center mast on which said annuli are mounted in a fixed position, annular insulators insulating annuli from the center mast and from one another, and fine wire ties looped around the filament strands and affixed on both sides thereof to the same annulus, ties of the same potential being affixed to the same annulus.

6. In an electron tube having anode and a filament within a vacuum envelope, a filament structure comprising a plurality of parallel filament strands circularly arranged and affixed to support and terminal means at one end, a center mast of refractory metal located on the tubes axis, supported at one end and having a reduced diameter at its other end, a close spaced pair of metallic annuli extending radially from the center mast, a tubular insulator which fits over the reduced diameter of the center mast and over which the annuli fit, larger diameter tubular insulators which fit over the tubular insulator and which insulate the annuli from each other and from the center mast, means engaging the center mast and bearing against the assembled insulators and annuli, thereby holding said assembly in place against the shoulder formed by the reduction in center mast diameter, and fine wire ties looped around the filament strands and aflixed on both sides thereof to the same annulus, ties of the same potential being afiixed to the same annulus.

'7. In an electron tube having an anode and a filament within a vacuum envelope, a filament structure comprising a plurality of parallel filament strands circularly arranged and afiixed to support and terminal means at one end, a center mast of refractory metal located on the tubes axis, supported at one end and having a reduced diameter at its other end, a close spaced pair of metallic annuli extending radially from the center mast, each annulus having radially extending legs at its outer edge, a tubular insulator which fits over the reduced diameter of the center mast and over which the annuli fit, larger diameter tubular insulators which fit over the tubular insulator and which insulate the annuli from each other and from the center mast, means engaging the center mast and bearing against the assembled insulators and annuli, thereby holding said assembly in place against the shoulder formed by the reduction in center mast diameter, and fine wire ties looped around the filament strands and afifixed on both sides thereof to a leg on one of the annuli, ties of the same potential being affixed to the same annulus.

8. In an electron tube having an anode and a filament within a vacuum envelope, a filament structure comprising a plurality of parallel filament strands circularly arranged and so connected that they permit a flow of current therethrough, a center mast of refractory metal supported at one end and located on the tubes axis,

close spaced pairs of metallic annuli extending radially from the center mast, annular insulators insulating each pair of annuli from the center mast and from each other, tubular separators which fit over the center mast and lie between adjacent pairs of annuli in order to maintain the relative position of said pairs of annuli, means at one end of the successive annuli assemblies and tubular separators holding them firmly against a shoulder at their opposite end, and fine wire ties looped around filament strands and affixed on both sides thereof to the same annulus, ties of the same potential being afiixed to the same annulus.

9. In an electron tube having an anode and a filament within a vacuum envelope, a filament structure comprising a plurality of parallel filament strands circularly arranged and so connected that they permit a flow of current therethrough, a sectional center mast of refractory metal supported at one end and located on the tubes axis, close spaced pairs of metallic annuli located at the junctions of the center mast sections and extending radially from the center mast, annular insulators insulating each pair of annuli from the center mast and from each other, opposing shoulders on the adjacent center mast sections which retain in place the annuli and the insulators, and fine wire ties looped around filament strands and afiixed on both sides thereof to the same radial flange, ties of the same potential being affixed to the same radial flange.

GEORGE J. AGULE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,819,146 Bol Aug. 18, 1931 2,330,401 Wing, Jr. Sept. 28, 1948 

